We are investigating the mechanism of site-specific recombination mediated by bacterial transposable elements. To this end we are creating mutants of the transposable kanamycin resistance element, Tn903, which are defective in transposition. These mutants will be used to determine which transposon-specified proteins are involved in the transposition process and in its control. We are also examining expression of the insertion element, IS1, to determine whether this small DNA segment (770 bp) encodes functions which activate translocation or other related processes.